The use of unmanned, remote-controlled machines for use in excavation is nothing new. But as robotics technology improves and new missions arise, these machines are evolving to keep pace. New scions of unmanned backhoes that can perform more intricate tasks - specifically, the ability to either navigate through an existing tunnel or actually dig the tunnel itself - are emerging. While many tunneling robots are still largely in their developmental stages, others have proven their worth in all-too-real scenarios such as mine disasters or building collapses. And perhaps one day, a robot will dig a tunnel through the martian ice and reveal thousands of years' worth of the Red Planet's geological history - including whether life exists or has ever existed there.

The engineers and scientists who work to develop tunneling robots face a wide array of hurdles. The devices have to be sturdy enough to work in temperature extremes, react to unexpected encumbrances or, once they have successfully traversed narrow passages, change jobs altogether from tunneling to something else, such as data collection. For the most part, it is too much to ask that tunneling robots do it all. Until miniaturization improves exponentially, most will likely rely on tethers to supply their power and enable data transfer, particularly when jobs require them to move long distances or through arduous environments. For the present, that seems to suit their designers fine.

'A Brick On An Icy Driveway' For geologists, permafrost polar ice provides a mother lode of information. The deeper they can penetrate and recover samples, the further they can look back in time.

On Earth, scientists can rely on a bevy of devices to dig into the polar ice caps, all from the relative comfort of a surface that at least has an atmosphere in which they can breathe and in which their tools' motors can operate.

Move the task to another heavenly body and the job becomes a bit trickier. For the past 28 years of his career at the Jet Propulsion Laboratory, Caltech science and instrument division in Pasadena, Calif., Wayne Zimmerman has headed the team working to accomplish exactly that. NASA scientists know the poles of Mars, as well as Europa, a moon of Jupiter, are covered with frozen slush. Knowing that nutrients essential to life tend to concentrate in strata of polar ice, researchers could possibly find the first hard evidence that life indeed exists elsewhere in the universe.

With a manned mission to Mars years away, NASA is sending a series of so-called "Scout" missions on relatively small, unmanned rockets to conduct preliminary research. Zimmerman has high hopes that a Scout mission in the near future will carry the cryobot he and his team have developed, which would be able to dig a tunnel into the ice of the martian north pole to send data home.

"You can learn a lot of things" from the ice, Zimmerman says. "For example, if there were a volcanic event on Mars, a deposition of material would get trapped in the polar ice, which consists of frozen water beneath a crust of frozen carbon dioxide. By understanding how much material is there, you come to understand how long the events went on."

The measurement of metals, ordered chemistries or material that fluoresces in the presence of an ultra-violet light source could provide clues to possible past or present biological activity, Zimmerman says. Originally designed for a possible NASA exploratory mission to Europa that was shelved, the cryobot garnered renewed interest when Mars exploration recently came to the forefront of NASA's goals.

"The weight of the probe is like a brick on an icy driveway," Zimmerman said. "The heat is transferred to the ice and slowly melts it. That's how it tunnels. There is no screw device, digging device or anything like that."

Should the probe veer off course, it can divert heat to one side, causing that side to melt ice more quickly. "That's how you steer the vehicle," Zimmerman says.

While the cryobot has yet to be deployed on a mission, Zimmerman and his team successfully tested a prototype in an Arctic glacier with a significant dust lode in 2001. The ice melted at a rate of 0.6-0.7 centimeters per hour, using only 0.5 kilowatts of power. "We know it works," Zimmerman says.